A shape of a general chain gear (or a sprocket) is a circle. A circular chain gear is easily produced and is thus generally much used. While a person rides and travels a bicycle, a force applied to a pedal is changed according to a position of a crank arm. That is, when a chain contacts with the shortest side, if the crank arm forms an angle of 30°-45° from a seat tube to which a saddle is coupled, a force ergonomically applying to the pedal extremely decreases, and if the crank arm forms an angle of about 165° from a seat tube, traveling inertia of the bicycle, angular acceleration of the crank, and ergonomics are combined and thus the crank arm is positioned at the longest side that may generate a largest force. Because such an ergonomical principle is not considered in a circular chain gear, traveling efficiency of the is bicycle is deteriorated.
In order to solve a problem, elliptical chain gears of several forms have been produced. Elliptical gears known up to now are greatly divided into a symmetrical elliptical gear and an asymmetrical elliptical gear. In a presently disclosed symmetrical elliptical gear, there is a merit that the elliptical gear can be easily produced, but at a partial segment in which a large force should be applied, as a gap between a crankshaft and a chain reduces, there is a defect that traveling efficiency decreases and shaking occurs and gear shifting is not smooth. In an existing asymmetric elliptical gear, such a problem can be somewhat solved, compared with a symmetrical elliptical gear, but it is not easy to produce the asymmetric elliptical gear and thus there is a defect that a production cost increases and an ergonomical principle is not accurately reflected, whereby the asymmetric elliptical gear still has a conventional problem.
U.S. Pat. No. 5,549,314 has a simple circular arc trajectory, which is a constant value at an angle 107° to 143° based on the shortest side, as shown in FIG. 8a, and a crank forms approximately 18° from the shortest side and thus when a chain contacts with the shortest side, a crank is positioned at a point in which a position of a saddle and a position of the crank correspond.
In U.S. Pat. No. 5,549,314, a crank position is formed by applying a is mathematical driving dead point concept, which is the hip joint center instead of a human body driving dead point concept formed with a hip joint, a knee joint, and an ankle joint, FIG. 8a illustrates a dead point position and FIG. 8b illustrates forming of the longest side, which is a maximum output segment, and a configuration of 107° is formed by adding traveling inertia that adds about 20° to a general angle 18° of a seat tube, an angle of less than 90°, which is a characteristic of a tangent, and a maximum output point.
U.S. Pat. No. 7,749,117 enables a dead point at which a chain is positioned at the shortest side to form an angle 30°-45° from a saddle using an accurate human body driving dead point concept, which is the knee joint center, as shown in FIG. 6a with a symmetrical elliptical gear, as shown in FIG. 9b and enables a maximum output segment to be positioned in an angle of 120°-130° from a saddle.
In U.S. Pat. No. 7,749,117, as the longest side, which is a maximum output segment is positioned in an angle of 120°-130° from a saddle, in the present invention, a position of the longest side, which is a substantial human body maximum output segment that applies acceleration and inertia is much short of an angle 165° from the saddle and an OCP system for overcoming this becomes a means that recognizes a limitation of a symmetrical gear.
As shown in FIG. 9d, in U.S. Pat. No. 5,549,314, even if a crank is angle is applied to a human body driving dead point, an angle between a longest side start point and a saddle becomes about 140°, and after the chain enters the longest side, h should reduce, and a human body resistance feeling becomes momentary damage at a constant value D segment, as shown in FIG. 10b, and a human body resistance feeling instantaneously rises so that a crank movement bottom dead point occurs.
The present invention provides an asymmetric elliptical gear that enables a constant value, which is a circular arc trajectory at the crank center that does not exist in a human body movement and a wrong dead point position of U.S. Pat. No. 5,549,314 not to exist and that enables a saddle to constantly maintain sensible resistance of a human body from 11 o'clock to 6 o'clock in a general bicycle of about an angle 18°, as shown in FIG. 9a by enabling to be adjacent to 135° instead of angle 90° between then long side and the short side, which is an insufficient congestion segment in U.S. Pat. No. 7,749,117.